Big plays have popped up here and there. The running game has flourished one week and withered the next. The quarterbacks have produced a few blossoms but little fruit.

The team's consistent offensive problems can be detailed through many statistical categories, but third-down-conversion percentage tells us all we need to know.

The Cardinals have converted 29.7 percent of the time. That ranks 30th in the NFL, behind only the 49ers and Rams.

"It's been pretty frustrating," offensive coordinator Mike Miller said. "It goes back to things we want to fix in our overall execution: the mental things we've had on third downs. And it's just guys making plays. We've had some things available.

"For one reason or another, everybody has taken a turn (making mistakes), me included."

The Cardinals struggle on other downs, so their poor conversion rate on third downs is a symptom, not the disease.

Diagnosing the cause of the actual illness isn't easy. It's like pinpointing the kid at daycare who first exposed everyone else to a nasty cold.

"Poor execution, that's most important," guard Daryn Colledge said. "Then early in the year, we had a lot of bad third-down situations: third and longs. And that's always going to be tough to convert.

"But third-and-1, third-and-2, those things have to be converted. If you get one guy missing his gap or one guy missing his block, you are not going to convert. That becomes a pattern. We know it's something we definitely have to improve upon."

When the vital signs of an offense are taken, third down is equivalent to blood pressure.

The Cardinals were terrible on offense in 2010 and converted on just 27.8 percent of third-down situations.

They are marginally better this year on offense, which is reflected in the disappointing 29.7 percent figure.

In 2008 and '09, the Cardinals' best offensive seasons under coach Ken Whisenhunt, the Cardinals had third-down percentages of 41.9 and 36.3.

Kurt Warner was the quarterback in those seasons, and the Cardinals haven't yet successfully replaced Warner.

Kevin Kolb's development has been hindered by a foot injury and now a concussion. His replacement, John Skelton, is in his second season and has been in and out of the lineup.

Those changes are among the reasons for the team's third-down performance, Whisenhunt said.

"You have your normal schemes on first and second downs and you're comfortable with those," Whisenhunt said. "Third downs have to change up every week because of the way the matchups go. You have to get comfortable with those plays.

"Different quarterbacks feel different with certain kinds of schemes. You plan for one, and then the other quarterback goes in. And he didn't get the reps at it, he doesn't see it, he doesn't feel the same way about it. There are a lot of variables."

Whisenhunt knows what all the above sounds like.

"It sounds like a bunch of excuses," he said, "and probably that's what it is. We need to just say, 'Look, we've got to operate better. You've got to stay with your reads, we've got to do a better job of protection and we've got to make those plays when they're there.' "